This invention relates to a dental tool for drilling (including cleaning) the dental root canal.
The dental root canal is an elongated passage which is narrow (typically being not more than 2 mm wide at its widest part) and is curved. In particular, it tends to be curved near its tip, which is where it is narrowest.
It is necessary to be able to clean debris out of the passage and it is also necessary to be able to prepare the passage, by drilling, for reception of a filling. Typically the prepared passage has an included angle in the range 10 to 15xc2x0 at its mouth end and of less than 2xc2x0, for instance around 1xc2x0, at its tip.
The root canal at present is generally cleaned and drilled using a solid file formed by twisting a square or triangular rod. The solid twisted rod has to be sufficiently thin and narrow that it can penetrate the canal. It has to withstand the repeated flexing that is caused by the curvature of the canal as the rod is rotated within it. Accordingly there is a risk of breakage.
In practice the file is usually rotated by hand, relatively slowly, and this minimises the problems of flexing and the risk of breakage. When the file is operated by a drill, for instance at 300 to 500 rpm, this causes very rapid flexing. This increases the risk of breakage of the file within the canal.
It is known to use an open helix, optionally coated with abrasive, as a paste filler or pulp extractor, for instance from DE-C-837146 and FR-B-901370, but these are not suitable for preparing the passage by drilling.
It is known from DE-A-37343003 to use a drill having a drilling head at the tip of a coil spring of uniform diameter, but this arrangement does not give effective drilling and cleaning, especially along the entire length, including in the narrow tip, of the canal and does not provide for removal of the debris.
In FR-A-2547718 the use of a tapered helix is described, with the helix surrounding a metallic filament. In theory this arrangement may be capable of giving some drilling and cleaning along the length of the canal but in practice it will be relatively ineffective because it does not provide any means for removing the debris from the canal. Thus if the drill is rotated so as to tighten the helix on to itself, rotation of the drill will merely force the debris further down into the canal. If the drill is rotated so as to loosen the helix, the helix is likely to become unwound and enlarged and will jamb in the root canal.
The purpose of the invention is to provide a root canal file by which it is possible to clean and drill the extremeties of the root canal and which will facilitate removal of debris from within the canal, and in particular to provide such a file which will achieve this object with minimum risk of breakage even when it is being rotated by a dental drill at, for instance, 500 rpm.
A dental root canal file according to the invention has a drilling end and a holder end interconnected by a shank. The drilling end and the shank have a maximum diameter of not more than 2 mm and are formed of a single hollow helix or are formed of two or more hollow helices which are co-wound and are interconnected substantially in end-to-end to relationship. The or each helix is a substantially closed hollow winding which can flex during drilling rotation and has an external surface which is abrasive to dental root canal material. Adjacent windings of the helix, or of at least one of the helixes, carry spacers whereby adjacent windings are in contact with each other but define openings between the windings.
The file can be fitted onto a stub of a conventional rotatable dental tool holder which can be mounted for rotation in conventional manner on a dental drill.
There is normally at least one internal lengthwise passage along the drilling end and the shank towards the holder end for the transfer of material towards the holder end or towards the drilling end. The holder into which the file can be fitted may include means for transferring material from or to this passage. For instance the holder may include means for applying suction to the passage so as to suck debris out of the canal or it may include means for forcing a fluid from the holder along the passage towards the tip, for irrigating the canal.